The present invention is directed, in particular, to a bonding process forming reliable intermetallic bonds one at a time between tape automated bonded ("TAB") leads and a suitable substrate or between TAB leads and integrated circuits. The process is thermosonic, using force, time, temperature and ultrasonic energy as the key parameters in forming the bonds. The key to the success of this process is the use of unique bonding tools designed to couple the ultrasonic energy into the lead efficiently and repeatedly.
There are several primary applications for this type of process. By forming the bonds individually with a small bonding tool, the problem of lack of planarity in gang (i.e., simultaneous bonding of a plurality of leads) TAB is eliminated. This is of most importance in outer lead bonding (OLB) of integrated circuit chips, for example, into a ceramic package where it is difficult to maintain sufficient flatness. This process is also useful for inner lead bonding (ILB), particularly for large devices or extremely sensitive devices such a GaAs integrated circuits. Due to the nature of the process, i.e., being single point bonding, it is very adaptable, which makes it desirable for short production runs, R & D work, and incoming material inspections.
One use of the present process is with a typical ceramic package such as a leadless chip carrier or pin grid array where absolute planarity of the package is not guaranteed. This technology is useful as a substitute for wire bonding in high density high lead count packages and in non-solderable environments such as hermetic packages and packages for military applications. Single point bonding is also useful in the repair of gang bonded devices and the assembly of short runs where set up of conventional TAB is not economically feasible.